In the scope of percutaneous medical procedures for diagnostic or therapeutic purposes, guided or not by imaging, an instrument likely to deform is introduced through the skin for reach a previously identified target. Different types of instruments are commonly used in daily medical practice for such interventions, such as for example probes, catheter guides, catheters, fibroscopes, probes, rods, and needles. For ease of execution of these procedures localisation and navigation tools have been developed for displaying, in real time and in a virtual environment representative of reality, the target, the position of the model of the instrument as well as its future trajectory.
The help given to the clinician by these novel tools allows him to guide the instrument to the target more precisely, resulting in a drop in morbidity. Yet, current localisation and navigation tools make the hypothesis of the indeformability of the instrument used, a hypothesis often not verified in current practice due to interactions of the instrument with human or animal tissue. In fact, interaction of the deformable instrument with human or animal tissue (soft tissue, hard osseous obstacle or other) is the origin of deformations of the instrument which can cause the interventional medical procedure to fail.
For example, interaction of the bevel of a straight flexible needle with tissue during deep biopsy can generate deflection responsible for failure of the puncture biopsy, with potential lesions of adjacent tissue (nerves, arteries). Inversely, the target can be mobilised following interaction of the instrument with human soft tissue originating in a failed procedure. Faced with these difficulties, it accordingly appears necessary to enrich the virtual environments of navigation representative of reality, by giving them the capacity to follow the exact position of the whole of the deformable instrument and deformed so as to specify in real time the relative positions of the instrument, of its distal end and of the target.
It would also be preferable to locally restrict the deformable instrument to correct its trajectory in light of reaching the target and improve the quality of the medical procedure. So, document U.S. Patent Publication No. 2005/0059883 describes the positioning of strain gauges on the proximal part of a flexible instrument, with a view to detecting the deflection of the instrument. The value of this deflection is taken into account by the navigation system to indicate the position of the distal end of the instrument. However, the type of device described takes into account only simple deformation (deflection) and not complex deformations (multiple curvatures), though more representative of reality, due to the unevenness of forces applied along the instrument. In addition, determining the position of the end of the instrument from data of proximal deformation presupposes a certain “regularity” of deformation of the instrument, in particular able to be incompatible with the very nature of the instrument (multiple curvatures). Finally, the proposed device is passive, that is, it does not modify the trajectory of the tool.
U.S. Pat. No. 5,830,144 provides for enclosing the tool in an elastomer or rigid sheath with a view to follow its position in real time. The sheath contains piezoelectric elements supplying a signal for detection of the position of the instrument by an echographic or electromagnetic localisation system. However, deformations of the instrument are not determined intrinsically at the instrument but extrinsically: the sheath, an element external to the instrument, must in effect be visible in real time by the localisation system to be able to identify its deformations, from which those of the instrument contained in the sheath are deduced. The necessity for visibility of the sheath within the tissue human constitutes a significant limitation of the device presented.
In addition, the quality of the junction between the sheath and the instrument appears to be essential to be able to deduce the position of the instrument from the position of the sheath. In fact, an instrument intended to pass through tissue naturally has a particularly smooth surface, but this surface state cannot ensure correct adherence of an attached element such as a sheath. Displacement of the sensors relative to the instrument can accordingly occur, causing imprecision in measuring, with potentially dramatic consequences for making gestures requiring much precision.
Document U.S. Pat. No. 7,261,686 proposes the use of a catheter guide comprising a plurality of actuators arranged over its length and a control unit of these actuators receiving information from strain gauges for example. In the proposed device, the catheter guide is introduced into a hollow anatomical structure the purpose of which is to deform to allow the catheter to move in the preferred direction. Once positioned, it can be “anchored” by modification of its rigidity. Highly useful for placing the catheter, this device requires control of direct imaging of the part within the organism. In addition, it permits only indirect guiding, by way of the guide, of the instrument (the catheter), and not direct navigation of the instrument inserted into the guide.
U.S. Patent Publication No. 2007/0016067 presents a robotised device for guiding a bevelled needle to a target by the combination of translation and rotation movements of the latter. This technique needs modelling of the mechanical tissular properties as well as detection of the needle and of its end on imaging acquired periodically. The use of a kinematic and not holonomic model associated with a careful combination of translation and rotation parameters of the needle helps correct the trajectory of the needle. However, using this method requires the capability of detecting the needle and its end, an easy process for X-ray imaging (fluoroscopic images) but which could be much more difficult for ultrasound imaging devices, for example (identification of the end of a needle also constitutes one of the difficulties of punctures guided under echographic imaging). In addition, for 2D echographic imaging this implicitly involves having positioning of the needle in the image acquisition plane.
In “‘Smart’ Needle for Percutaneous Surgery: Influential Factor Investigation”, of Yan et al. (Proceedings of the 29th Annual international Conference of the IEEE EMBS, Aug. 23-26, 2007), the authors are interested in knowledge of the deflection of a needle and of its mobilisation by the use of piezoelectric actuators. In the approach presented, the end of the needle is detected by use of an electromagnetic sensor arranged at the end of the needle. In this case, it is however necessary to have direct display of the needle to act appropriately. The current limitations of electromagnetic localisation systems should also be pointed out.
A first aim of the invention is to propose a device capable of taking into account complex deformations, and a fortiori simple deformations, of an instrument intended to pass through human or animal tissue. Such a device should be able to know, at any time and using a localisation or navigation system, the position of the distal end of the instrument relative to its proximal part, and/or the position of the whole instrument potentially deformed relative to its proximal part. Another aim of the invention is to locally restrict the deformable instrument in light of facilitating its being guided to the target.